What observation led Wilhelm Conrad Roentgen to discover X-rays in 1895?

Answer

A fluorescent glow

While experimenting with a cathode ray tube, Roentgen observed a mysterious fluorescence. This phenomenon indicated the presence of a previously unknown form of energy. He identified these emissions as X-rays, recognizing their unique ability to penetrate physical matter, which fundamentally transformed the field of modern medicine and diagnostics.

What observation led Wilhelm Conrad Roentgen to discover X-rays in 1895?
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